The present invention relates to a method of electronically controlling a vehicle.
Vehicles, typically automobiles, powered by internal combustion engines have a transmission coupled between the engine and driven wheels for effective utilization of output power from the engine. In operation, one of different gear ratios of the transmission is selected to meet the particular vehicle speed. For example, when the vehicle is to run at a low speed, a larger gear ratio of the transmission is used.
In a recently developed transmission system, use is made of a hydraulic drive mechanism controlled by a computerized electronic control unit to automatically drive an internal lever which controls a disk clutch and selects transmission gears. The system has a select actuator for operating the clutch actuator of the hydraulic drive in such a manner that the disk clutch is operated as if by a human foot, and for driving the interval lever selectively in a Y direction, as well as a shift actuator for driving the internal lever in an X direction perpendicular to the Y direction. The computerized electronic control unit has a memory for storing data known as a shift map representing transmission stages corresponding to automobile speeds and degrees of depression of an accelerator pedal. While the automobile is being driven, the electronic control unit detects the vehicle speed and depression of the accelerator pedal at all times and searches the shift map based on these data to determine an optimum transmission gear. Then, the electronic control unit issues a command to operate the shift actuator and select actuator alternatingly to thereby select an optimum transmission gear ratio.
Let us investigate an automobile equipped with the electronic control unit in a situation where the automobile is at rest following the completion of forward motion. The engine will be idling, the transmission will be in neutral, and the disk clutch will be in the disengaged state. However, when the transmission is in neutral, the transmission counter shaft is capable of rotating freely so that there are cases where the disk clutch, though disengaged, is still pressed against a pressure plate or flywheel. In consequence, the transmission counter shaft is rotated by the engine. In addition, even if the clutch is completely disengaged immediately after the forwardly traveling automobile is stopped, the counter shaft continues rotating for a time because of inertia. To drive the automobile in reverse starting from the condition of the automobile just described, the driver switches the shift lever to the reverse position, whereupon the electronic control unit issues a command to operate the shift actuator and select actuator alternatingly in an effort to mesh the main shaft gear of the transmission with the reverse idle gear. In this operation, the stationary main shaft gear is made to mesh with the reverse idle gear, which is rotating together with the counter shaft, and the disk clutch is made to separate from the pressure plate or flywheel. As a result, the main shaft gear is subjected to an excessive load and, during the shifting operation, not only produces annoying noise but sustains considerable wear. Though this problem can be solved by providing the reverse position gear mechanism with a synchromesh mechanism, redesigning and manufacturing the gear mechanism anew would entail an increase in cost. Another disadvantage is that it would be unable to utilize the conventionally employed transmission.